Folate deficiency has been implicated in epidemiologic, genomic, and neuroimaging studies of schizophrenia. Patients with schizophrenia exhibit low blood folate levels that correlate with negative symptom severity, a pattern that is strongly influenced by variation in folate-related genes. Two recent clinical trial by our group demonstrated a benefit of folate supplementation for negative symptoms, but only among patients who carried the previously implicated genetic variants. We have also seen consistent effects of folate-related genes on functional and structural MRI measures within the frontoparietal control network, in both patients with schizophrenia and healthy individuals. This work suggests that (1) folate-related genes exert important clinical effects in schizophrenia that are relevant to treatment response, and (2) these genes influence brain systems that underlie treatment-refractory aspects of schizophrenia. However, the effects of genetic variation across the folate metabolic pathway on the brain remain incompletely characterized, as does the relationship between dietary folate intake and brain structure and function. Also, importantly, the clinical benefit of folate supplementation in schizophrenia was relatively modest, even among individuals who carried predisposing genetic variants. Earlier exposure to folate augmentation, including during neurodevelopment, may confer a stronger benefit for at-risk individuals. Indeed, recent studies suggest that increased maternal folate intake early in pregnancy can reduce the risk of autism, especially among mothers who have low-functioning genetic variants in the folate metabolic pathway. The proposed study of healthy adults and adolescents will greatly extend our understanding of how folate influences the brain, as a prelude to developing improved folate-based interventions. We will focus on structural and functional measures in the frontoparietal control system that are consistently abnormal in schizophrenia, and that have been tied to folate-related genes. For Aim 1, we will leverage a large, existing collection of MRI data and DNA (>3,300 subjects) to conduct novel, polygene-score based analyses of genetic variation throughout the folate metabolic pathway. In Aim 2, we will recruit individuals across a range of polygene scores to determine how folate intake influences high-resolution structural and functional MRI indices. Using the same MRI measures, Aim 3 will leverage a recent large-scale public health intervention to examine effects of in utero folate exposure in two age-matched cohorts of healthy adolescents: one group will have gestated before mandatory folate fortification of grain products was implemented in 1998, and the other will have gestated after this intervention. This multi-tiered approach will allow us to comprehensively evaluate genomic (Aim 1), environmental (Aim 2), and neurodevelopmental (Aim 3) aspects of folate effects on the brain, both separately and in combination with each other. This work could have important implications for the use of targeted, high-dose folate augmentation as a preventative strategy, especially among young individuals at high risk for schizophrenia, or even pre-conception.